Superconducting accelerating cavity and electropolishing method for superconducting accelerating cavity

ABSTRACT

Provided is a superconducting accelerating cavity  30  including: a cavity main body  10  formed of a superconducting material into a cylindrical shape; and a refrigerant tank  20  installed around the cavity main body  10  and storing a refrigerant which is supplied from the outside through a supply port  20   a  into a space formed between the refrigerant tank and the outer circumferential surface of the cavity main body  10 , wherein the outer circumferential surface of the cavity main body  10  is coated with a metal coating layer  10   a  having a higher conductivity than the superconducting material.

TECHNICAL FIELD

The present invention relates to a superconducting accelerating cavityand an electropolishing method for a superconducting acceleratingcavity.

BACKGROUND ART

A superconducting accelerating cavity is a device for acceleratingcharged particles such as electrons, positrons, and protons by means ofan accelerating electric field generated inside the cavity by an inputof high-frequency power. When the inner surface of the main body of thesuperconducting accelerating cavity is not smooth, or when impuritiesare present on the inner surface of the main body, heat generation orelectrical discharge is induced, which degrades the performance ofaccelerating the charged particles.

It is a known practice to perform electropolishing in order to smooththe inner surface of the main body of the superconducting acceleratingcavity and remove impurities from the inner surface (e.g., see PTL 1).Eiectropolishing of the superconducting accelerating cavity is performedwith an electrode installed on each of the inside of the cavity mainbody and the outer surface of the cavity main body, while the cavitymain body is filled with an electrolyte.

CITATION LIST Patent Literature

-   PTL 1-   Japanese Unexamined Patent Application, Publication No. 2000-123998-   PTL 2-   The Publication of Japanese Patent No. 3416249

SUMMARY OF INVENTION Technical Problem

After electropolishing is performed, a refrigerant tank which stores arefrigerant such as liquid helium for cooling the superconductingaccelerating cavity is installed around the main body of thesuperconducting accelerating cavity. In order to prevent leakage of therefrigerant, etc, this refrigerant tank is installed by firmly joiningmultiple members by welding, etc., which are arranged so as to cover thecircumference of the superconducting accelerating cavity, (e.g., see PTL2).

The inner surface of the superconducting accelerating cavity after beingelectropolished is smooth and free of impurities. However, there is apossibility of foreign substances such as dirt entering into the mainbody of the superconducting accelerating cavity during mounting of aninlet pipe, through which charged particles from the outside are guided,and an outlet pipe, which guides the charged particles to the outside,to the main body of the superconducting accelerating cavity. Onceforeign substances such as dirt enter into the main body of thesuperconducting accelerating cavity, heat generation or electricaldischarge is induced, which degrades the performance of thesuperconducting accelerating cavity. This performance degradationproblem can be solved by performing electropolishing again to smooth theinner surface of the main body of the superconducting acceleratingcavity.

There is a problem, however/that due to the difficulty of installingelectrodes at arbitrary positions on the outer surface of the cavitymain body after the refrigerant tank is installed around the main bodyof the superconducting accelerating cavity, the degree of polishing ofelectropolishing becomes non-uniform depending on the presence orabsence of contact with (contact state of) the electrode. Thus, it isnot easy, after installation of the refrigerant tank around the mainbody of the superconducting accelerating cavity, to electropolish themain body of the superconducting accelerating cavity again to a uniform,degree without removing the refrigerant tank.

Having been made in view of these circumstances, the present inventionhas an object to provide a superconducting accelerating cavity which canbe easily electro-polished again even after installation of arefrigerant tank, and an electropolishing method for a superconductingaccelerating cavity.

Solution to Problem

To achieve the above object, the present invention has adopted thefollowing solutions:

The superconducting accelerating cavity according to the presentinvention includes: a cavity main body formed of a superconductingmaterial into a cylindrical shape; and a refrigerant tank installedaround the cavity main body and storing a refrigerant which is suppliedfrom the outside through a supply port into a space created between therefrigerant tank and the outer circumferential surface of the cavitymain body, wherein the outer circumferential surface of the cavity mainbody is coated with a metal material having a higher conductivity thanthe superconducting material.

In the superconducting accelerating cavity according to the presentinvention, the refrigerant tank is installed around the cavity main bodywhich is formed of a superconducting material into a cylindrical shape.This refrigerant tank is provided with the supply port through which arefrigerant is supplied from the outside, and anode parts connected to apositive pole of a power source can be inserted into the refrigeranttank through the supply port. Since the outer circumferential surface ofthe cavity main body is coated with a metal material having a higherconductivity than the superconducting material, bringing the anode partsinserted inside the refrigerant tank into contact with the outercircumferential surface of the cavity main body allows the cavity mainbody to be uniformly anodized for electropolishing.

Then, a cathode part connected to a negative pole of the power source isinserted inside the cavity main body and the electrolyte is suppliedinto the cavity main body, so that the inner surface of the cavity mainbody can be electropolished.

Thus, according to the superconducting accelerating cavity of thepresent invention, it is possible to provide a superconductingaccelerating cavity which can be easily electropolished again even afterinstallation of the refrigerant tank.

In a superconducting accelerating cavity of a first aspect of thepresent invention, the cavity main body has a shape formed by largediameter portions and small diameter portions, which are at a shorterdistance to the central axis of the cavity main body than the largediameter portions, being alternately formed along the axial direction,and the position of the supply port in the axial direction correspondsto the position of the large diameter portion in the axial direction.

In this way, the anode parts which are inserted from the supply port canfoe easily brought into contact with the large diameter portion of thecavity main body which is disposed at the position close to the supplyport of the refrigerant tank.

In a superconducting accelerating cavity of a second aspect of thepresent invention, the cavity main body has a shape formed by largediameter portions and small diameter portions, which are at a shorterdistance to the central axis of the cavity main body than the largediameter portions, being alternately formed along the axial direction,and the coating thickness of the metal material in the large diameterportions is larger than the coating thickness of the metal material inthe small diameter portions.

In this way, current can flow more easily in the large diameter portionswhich are farther away from the central axis of the cavity main body, inwhich the cathode is disposed during electropolishing, than in the smalldiameter portions which are closer to the central axis. Thus, the defectof the degree of polishing of electropolishing becoming non-uniform onthe inner surface of the cavity main body can be suppressed.

In the superconducting accelerating cavity of the second aspect of thepresent invention, the ratio between the distance to the central axis ofthe large diameter portions and the distance to the central axis of thesmall, diameter portions/and the ratio between the coating thickness inthe large diameter portions and the coating thickness in the smalldiameter portions may substantially correspond to each other.

In this way, the coating thickness in the large diameter portions andthe coating thickness in the small diameter portions of the cavity mainbody can be adjusted to a proper coating thickness according to thedistance from the central axis of the cavity main body in which thecathode is disposed during electropolishing.

An electropolishing method for a superconducting accelerating cavity ofthe present invention is an electropolishing method for asuperconducting accelerating cavity which includes: a cavity main bodyformed of a superconducting material into a cylindrical shape; and arefrigerant tank installed around the cavity main body and storing arefrigerant which is supplied from the outside through a supply portinto a space created between the refrigerant tank and the outercircumferential surface of the cavity main body, the outercircumferential surface of the cavity main body being coated with ametal material having a higher conductivity than the superconductingmaterial, wherein the electropolishing method includes: inserting ananode part which is connected to a positive pole of a power sourcethrough the supply port and bringing the anode part into contact withthe outer circumferential surface of the cavity main body; inserting acathode part which is connected to a negative pole of the power sourceinto the cavity main body; supplying an electrolyte into the cavity mainbody; and starting energization by the power source and electropolishingthe inner surface of the cavity main body.

According to the electropolishing method of the present invention, sincethe outer circumferential surface of the cavity main body is coated witha metal material having a higher conductivity than the superconductingmaterial, bringing the anode part into contact with the outercircumferential surface of the cavity main body by the anodeinstallation step allows the cavity main body to be uniformly anodizedfor electropolishing.

Then, the cathode part connected to the negative pole of the powersource is inserted inside the cavity main body by the cathodeinstallation step and the electrolyte is supplied into the cavity mainbody by the supply step, so that the inner surface of the cavity mainbody can be electropolished.

Thus, according to the electropolishing method for a superconductingaccelerating cavity of the present invention, it is possible to providean electropolishing method for a superconducting accelerating cavity bywhich electropolishing can be easily performed again even afterinstallation of the refrigerant tank.

In an electropolishing method for a superconducting accelerating cavityof a first aspect of the present invention, the cavity main body has ashape formed by large diameter portions and small diameter portions,which are at a shorter distance to the central axis of the cavity mainbody than the large diameter portions, being alternately formed alongthe axial direction, and the position of the supply port in the axialdirection corresponds to the position of the large diameter portion inthe axial direction.

In this way, the anode part which is inserted from the supply port canbe easily brought into contact with the large diameter portion of thecavity main body which is disposed at the position close to the supplyport of the refrigerant tank.

In an electropolishing method for a superconducting accelerating cavityof a second aspect of the present invention, the cavity main body has ashape formed by large diameter portions and small diameter portions,which are at a shorter distance to the central axis of the cavity mainbody than the large diameter portions, being alternately formed alongthe axial direction, and the coating thickness of the metal material inthe large diameter portions is larger than the coating thickness of themetal material in the small diameter portions.

In this way, current can flow more easily in the large diameter portionswhich are farther away from the central axis of the cavity main body, inwhich the cathode is disposed during electropolishing, than in the smalldiameter portions which are closer to the central axis. Thus, the defectof the degree of polishing of electropolishing becoming non-uniform onthe inner surface of the cavity main body can be suppressed.

In an electropolishing method for a superconducting accelerating cavityof a third aspect of the present invention, the ratio between thedistance to the central axis of the large diameter portions and thedistance to the central axis of the small diameter portions, and theratio between the coating thickness in the large diameter portions andthe coating thickness in the small diameter portions may substantiallycorrespond to each other.

In this way, the coating thickness in the large diameter portions andthe coating thickness in the small diameter portions of the cavity mainbody can be adjusted to a proper coating thickness according to thedistance from the central axis of the cavity main body in which thecathode is disposed during electropolishing.

Advantageous Effects of Invention

According to the present invention, it is possible to provide asuperconducting accelerating cavity which can be easily electropolishedagain even after installation of a refrigerant tank, and anelectropolishing method for a superconducting accelerating cavity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view showing the configurationof a superconducting accelerator of a first embodiment of the presentinvention.

FIG. 2 is a longitudinal cross-sectional view showing a superconductingaccelerating cavity and an electropolishing device of the firstembodiment of the present invention.

FIG. 3 is a flowchart showing an electropolishing method for asuperconducting accelerating cavity of the first embodiment of thepresent invention.

FIG. 4 is a view showing a modified example of an anode part installed,in a refrigerant tank.

FIG. 5 is a view showing another modified example of the anode partinstalled in the refrigerant tank.

FIG. 6 is a view showing a cavity main body of a superconductingaccelerating cavity of a second embodiment of the present invention.

FIG. 7 is a cross-sectional view along the arrow A-A of thesuperconducting accelerating cavity and the electropolishing deviceshown in FIG. 2.

DESCRIPTION OF EMBODIMENTS First Embodiment

In the following, a superconducting accelerator 100 of a firstembodiment of the present invention will be described by using FIG. 1.FIG. 1 is a longitudinal cross-sectional view showing the configurationof the superconducting accelerator of the first embodiment of thepresent invention.

In FIG. 1, the superconducting accelerator 100 includes asuperconducting accelerating cavity 30, and a vacuum vessel 90 housingthe superconducting accelerating cavity 30. The superconductingaccelerating cavity 30 includes a cavity main body 10 formed of asuperconducting material such as niobium (Nb) into a cylindrical shape,and a refrigerant tank 20 installed around the cavity main body 10. Therefrigerant tank 20 stores a refrigerant which is supplied from theoutside through a supply port 20 a into a space created between therefrigerant tank and the outer circumferential surface of the cavitymain body 10. As the refrigerant, for example, liquid helium is used.

The outer circumferential surface of the cavity main body 10 is coatedwith a metal material having a higher conductivity than thesuperconducting material. This coated part forms a metal coating layer10 a. As the metal material having a high conductivity, for example,copper, gold, silver, or aluminum is used. The reason for coating theouter circumferential surface of the cavity main body 10 with a metalmaterial having a high conductivity is, as described later, to make thecavity main body 10 function as an anode during electropolishing. Inthis embodiment, the coating thickness of the metal coating layer 10 ashall be substantially constant regardless of the position in thedirection of the central axis of the cavity main body 10. A constantcoating thickness of the metal coating layer 10 a allows a substantiallyconstant potential to be applied to the entire cavity main body 10.

The cavity main body 10 have equatorial portions (large diameterportions) 10 d, 10 e, 10 f, and 10 g at a distance R1 from a centralaxis A. In addition, the cavity main body 10 have iris portions (smalldiameter portions) 10 h, 10 i, and 10 j at a distance R2 from thecentral axis A. As shown in FIG. 1, the distance R2 to the central axisA of the iris portions 10 h, 10 i, and 10 j is shorter than the distanceR1 to the central axis A of the equatorial portions 10 d, 10 e, 10 f,and 10 g. As shown in FIG. 1, the cavity main body 10 has a shapeformed, by the equatorial portions 10 d, 10 e, 10 f, and 10 g, and theiris portions 10 h, 10 i, and 10 j being alternately formed along thedirection of the central axis A.

Since the refrigerant is stored in the refrigerant tank 20, therefrigerant tank 20 and the cavity main body 10 are firmly joined bywelding, etc. at areas contacting with each other. Due to such astructure, it is difficult to remove the refrigerant tank 20 from thecavity main body 10 after the refrigerant tank 20 is joined to thecavity main body 10.

The supply port 20 a is connected with a supply pipe 40 which suppliesthe refrigerant. The supply pipe 40 is a pipe for supplying therefrigerant, which is supplied from an external refrigerant tank (notshown), to the supply port 20 a. Liquid helium supplied from the supplypipe 40 and stored in the refrigerant tank 20 is used for cooling thecavity main body 10 to an ultralow temperature and keep the cavity mainbody in a superconducting state.

Part of the liquid helium stored in the refrigerant tank 20 absorbs theheat generated in the cavity main body 10 and is gasified into a heliumgas. The helium gas is discharged from a discharge port 20 b to theoutside of the superconducting accelerating cavity 30, and is dischargedto the outside of the superconducting accelerator 100 through adischarge pipe 50. The helium gas discharged to the outside isreliquefied by being compressed by a compressor (not shown.) andreturned to the refrigerant tank.

The position of the supply port 20 a of the refrigerant tank 20 in thedirection of the central axis A corresponds to the position of theequatorial portion 10 d. In addition, the position of the discharge port20 b of the refrigerant tank 20 corresponds to the position of theequatorial portion 10 g. The reason for this arrangement is, asdescribed later, to make it easier to bring anode parts 230 and 240 tobe inserted from the supply port 20 a and the discharge port 20 b intocontact with the metal coating layer 10 a formed on the outercircumferential surface of the cavity main body 10 when the cavity mainbody 10 is made to function as an anode for electropolishing.

The cavity main body 10 is provided with an inlet part 10 c and anoutlet part 10 b, which are openings, at both ends in the direction ofthe central axis. The inlet part 10 c is connected with an inlet pipe 70through which charged particles from the outside are guided, and theinlet part 10 c guides the charged particles guided through the inletpipe 70 to the cavity main body 10. The outlet part 10 b is connectedwith an outlet pipe 80 which guides the charged particles to theoutside, and the outlet part 10 b guides the charged particlesaccelerated in the cavity main body 10 to the outlet pipe 80.

A waveguide 60, which is provided so as to foe connected with the outletpart 10 b of the cavity main body 10, is a pipe for introducinghigh-frequency power generated by a high frequency source (not shown)such as a klystron into the cavity main body 10. When high-frequencypower is input from the outside through the waveguide 60, a positiveelectrode and a negative electrode are generated on the inner surface ofthe cavity main body 10, and an accelerating electric field foraccelerating the charged particles is produced.

The superconducting accelerating cavity 30 is disposed inside the vacuumvessel 90. The inside of the vacuum vessel 90 is maintained in asubstantially vacuum state by a vacuum device (not shown), and thevacuum vessel 90 prevents external heat from transferring to thesuperconducting accelerating cavity 30.

Next, an electropolishing device 200 of this embodiment will bedescribed by using FIG. 2. FIG. 2 is a longitudinal cross-sectional viewshowing the superconducting accelerating cavity 30 and theelectropolishing device 200 of this embodiment. The electropolishingdevice 200 is constituted of the parts excluding the superconductingaccelerating cavity 30 shown in the configuration of FIG. 2. In FIG. 2,a pair of rotation holding tools 300 which is shown in FIG. 7 anddescribed later is not shown.

The electropolishing device 200 includes: an electrolyte supply device210 which circulates the electrolyte inside the cavity main body 10; acathode part 220 disposed inside the cavity main body 10; the anode part230 inserted in the supply port 20 a of the refrigerant tank 20; and theanode part 240 inserted in the discharge port 20 b of the refrigeranttank 20. The cathode part 220 is connected to the negative pole of thepower source 250, while the anode parts 230 and 240 are connected to thepositive pole of the power source 250. The current supply from the powersource 250 to each electrode can be switched on and off by the switch260.

Caps 270 and 271 for preventing leakage of the electrolyte are attachedto the respective ends of the cavity main body 10. The cathode part 220,which is a hollow cylindrical member, is supported by the cap 270 andthe cap 271 at both ends so as to be disposed coaxially with the centralaxis of the cavity main body 10. Actuating a pump 280 causes theelectrolyte inside a tank 290 to be supplied into the cathode part 220through the cap 270. As the electrolyte, various electrolytes can beused; for example, hydrogen fluoride, sulfuric acid, etc. are used.

The cathode part 220 which is a hollow cylindrical member is providedwith multiple openings 220 a. The electrolyte flowing inside the cathodepart 220 flows out through the multiple openings 220 a into the cavitymain body 10, and the electrolyte is supplied into the cavity main body10. The electrolyte which flows inside the cathode part 220 withoutflowing out through the openings 220 a is returned via the cap 271 tothe tank 290.

The anode part 230 is constituted of a cable connection part 231, a rodpart 232, a contact part 233, and a cap 234, Each member constitutingthe anode part 230 is constituted of a metal having a high conductivitysuch as copper. Each member constituting the anode part 230 issubstantially at the same potential as the positive pole of the powersource 250.

A cable coupled with the positive pole of the power source 250 isconnected to the cable connection part 231. The cable connection part231 is coupled with the rod part 232, and the rod part 232 is coupledwith the contact part 233. The rod part 232 is a rod-like member with amale thread formed on the outer circumferential surface, and is engagedwith a female thread formed on the inner circumferential surface of ahole provided at the center part of the cap 234. The cap 234 is fastenedwith a bolt to a flange which is provided at the supply port 20 a of therefrigerant tank 20.

Rotating the cable connection part 231 coupled with the rod part 232causes the rod part 232 to move in the axial direction of the rod part232 relative to the cap 234. In accordance with this movement, thecontact part 233 coupled with the leading end of the rod part 232 ismoved closer to or away from the metal coating layer 10 a provided onthe outer circumferential surface of the equatorial portion 10 d of thecavity main body 10.

Fastening the cap 234 with a bolt to the flange provided at the supplyport 20 a of the refrigerant tank 20 and rotating the cable connectionpart 231 can bring the contact part 233 gradually closer to the metalcoating layer 10 a. The contact part 233 is adjusted so as to come intocontact with the metal coating layer 10 a provided on the outercircumferential surface of the equatorial portion 10 d of the cavitymain body 10. In this way, the positive pole of the power source 250 andthe metal coating layer 10 a are electrically connected, so that themetal coating layer 10 a functions as an anode for electropolishing.

The anode part 240 is constituted of a cable connection part 241, a rodpart 242, a contact part 243, and a cap 244. Each member constitutingthe anode part 240 is constituted of a metal having a high conductivitysuch as copper. Each member constituting the anode part 240 issubstantially at the same potential as the positive pole of the powersource 250.

A cable coupled with the positive pole of the power source 250 isconnected to the cable connection part 241. The cable connection part241 is coupled with the rod part 242, and the rod part 242 is coupledwith the contact part 243. The rod part 242 is a rod-like member with amale thread formed on the outer circumferential surface, and is engagedwith a female thread formed on the inner circumferential surface of ahole provided at the center part of the cap 244. The cap 244 is fastenedwith a bolt to a flange provided at the discharge port 20 b of therefrigerant tank 20.

Rotating the cable connection part 241 coupled with the rod part 242causes the rod part 242 to move in the axial direction of the rod part242 relative to the cap 244. In accordance with this movement, thecontact part 243 coupled with the leading end of the rod part 242 ismoved closer to or away from the metal coating layer 10 a provided onthe outer circumferential surface of the equatorial portion 10 g of thecavity main body 10.

Fastening the cap 244 with a bolt to the flange provided at thedischarge port 20 b of the refrigerant tank 20 and rotating the cableconnection part 241 can bring the contact part 243 gradually closer tothe metal coating layer 10 a. The contact part 243 is adjusted so as tocome into contact with the metal coating layer 10 a provided on theouter circumferential surface of the equatorial portion 10 g of thecavity main body 10. In this way, the positive pole of the power source250 and the metal coating layer 10 a are electrically connected, so thatthe metal coating layer 10 a functions as an anode for electropolishing.

As shown in FIG. 7, the electropolishing device 200 includes the pair ofrotation holding tools 300 which rotatably holds the superconductingaccelerating cavity 30 around the central axis A, and a rotation device(not shown) which rotates the superconducting accelerating cavity 30,which is held by the rotation holding tools 300, around the central axisA. FIG. 7 is a cross-sectional view along the arrow A-A of thesuperconducting accelerating cavity 30 and the electropolishing device200 shown in FIG. 2.

The rotation holding tool 300 includes an annular rail part 310 disposedin a plane perpendicular to the central axis A, and support parts 320and 330 supporting the rail part 310 against a ground surface G. Thesupport parts 320 and 330 fix the rail part 310 relative to the groundsurface G. Although FIG. 7 shows the rotation holding tool 300 which ispresent at the position of the anode part 230, the other rotationholding tool 300 is present at the position of the anode part 240.

Thus, the superconducting accelerating cavity 30 is held relative to theground surface G by the pair of rotation holding tools 300 disposed atthe position of the anode part 230 and the position of the anode part240. The superconducting accelerating cavity 30 held by the pair ofrotation holding tools 300 is rotated around the central axis A by therotation device (not shown).

The rotation device includes a motor (not shown) which rotates a gearcoupled with another gear (not shown) provided on the outercircumferential surface of the superconducting accelerating cavity 30.Rotating the motor causes the superconducting accelerating cavity 30 torotate around the central axis A.

The cable connection part 231 of the anode part 230 is a rotating memberwhich rotates while being engaged with the rail part 310. In addition,the cable connection part 231 is electrically connected with thepositive pole of the power source 250, which is connected to the outercircumferential surface of the rail part 310, through the conductiverail part 310.

Thus, rotating the superconducting accelerating cavity 30 allows theelectrolyte to spread over the entire inner surface of the cavity mainbody 10, so that the inner surface is uniformly electropolished.

Next, an electropolishing method of this embodiment will be described byusing FIG. 3. FIG. 3 is a flowchart showing the electropolishing methodfor the superconducting accelerating cavity 30 of this embodiment. Theelectropolishing method of this embodiment is performed in such a casewhere, after the superconducting accelerating cavity 30 is integratedinto the superconducting accelerator 100 shown in FIG. 1 and thesuperconducting accelerator 100 is operated, inclusion of foreignsubstances inside the superconducting accelerating cavity 30 issuspected as a result of a measurement.

The superconducting accelerating cavity 30 is supposed to be removed tothe outside of the vacuum vessel 90 from the superconducting accelerator100 shown in FIG. 1 before the electropolishing method of thisembodiment is performed.

Step S301 is an anode installation step of installing the anode part 230in the supply port 20 a of the refrigerant tank 20 and installing theanode part 240 in the discharge port 20 b of the refrigerant tank 20.The anode part 230 is installed in the supply port 20 a, and the cableconnection part 231 is rotated to adjust the position of the contactpart 233, and the contact part 233 is brought into contact with themetal coating layer 10 a of the cavity main body 10. In the same way,the anode part 240 is installed in the discharge port 20 b, and thecable connection part 241 is rotated to adjust the position of thecontact part 243, and the contact part 243 is brought into contact withthe metal coating layer 10 a of the cavity main body 10.

Thus, the anode installation step S301 is a step of inserting the anodepart 230, which is connected to the positive pole of the power source250, from the supply port 20 a and bringing the anode part 230 intocontact with the metal coating layer 10 a on the outer circumferentialsurface of the cavity main body 10. In addition, the anode installationstep 3301 is a step of inserting the anode part 240, which is connectedto the positive pole of the power source 250, from the discharge port 20b and bringing the anode part 240 into contact with the metal coatinglayer 10 a on the outer circumferential surface of the cavity main body10. Performing the anode installation step S301 causes the positive poleof the power source 250 and the metal coating layer 10 a to beelectrically connected, so that the metal coating layer 10 a functionsas an anode for electropolishing.

Step S302 is a cathode installation step of installing the cathode part220 coaxially with the central axis of the cavity main body 10. Thecathode part 220 is inserted into the cavity main body 10, and the cap270 is installed at the outlet part 10 b of the cavity main body 10,while the cap 271 is installed at the inlet part 10 c of the cavity mainbody 10, and thereby the cathode part 220 is installed coaxially withthe central axis of the cavity main body 10. After the cathode part 220is installed, the caps 270 and 271 are connected with the pipe of theelectrolyte supply device 210 so that the electrolyte can be supplied bythe electrolyte supply device 210. In addition, the negative pole of thepower source 250 and the cathode part 220 are electrically connected sothat the cathode functions as a cathode for electropolishing.

Step S303 is an electrolyte supply step of supplying the electrolyteinto the cavity main body 10. The pump 280 of the electrolyte supplydevice 210 is driven and the electrolyte inside the tank 290 is suppliedto the cathode part 220, and thereby the electrolyte is supplied throughthe openings 220 a into the cavity main body 10. When the amount ofelectrolyte supplied into the cavity main body 10 has reached apredetermined amount, driving of the pump 280 is stopped to stop theelectrolyte supply to the cavity main body 10.

Step S304 is an electropolishing step of electropolishing the cavitymain body 10 in which the anode parts 230 and 240 and the cathode part220 are installed and the electrolyte is supplied to the inside. In stepS304, the switch 260 is switched, from the off state to the on state.Switching the switch 260 to the on state brings the anode parts 230 and240 to the same potential as the positive pole of the power source 250,and the cathode part 220 to the same potential as the negative pole ofthe power source 250, turning the cathode part into a cathode.

Since the anode parts 230 and 240 are in contact with the metal coatinglayer 10 a on the outer circumferential surface of the cavity main body10, the entire metal coating layer 10 a functions as an anode. Since thecathode part 220 is constituted of a conductive metal material over theentire length in the axial direction, the cathode part 220 functions asa cathode over the entire length in the axial direction. Thus, currentflows through the electrolyte between the cathode part 220 and the innercircumferential surface of the cavity main body 10 over the entirelength of the cathode part 220 in the axial direction, causingelectrolysis of the electrolyte. The inner circumferential surface ofthe cavity main body 10 is polished due to this electrolysis.

While the electropolishing step S304 is in progress, the superconductingaccelerating cavity 30 is kept rotating around the axis by the rotationdevice. Rotating the superconducting accelerating cavity 30 allows theelectrolyte to spread over the entire inner surface of the cavity mainbody 10, so that the inner surface is uniformly electropolished. Theamount of polishing achieved in the electropolishing step S304 can beadjusted by adjusting the output voltage of the power source 250 or thetime of electropolishing, and the amount of polishing is, for example,set to approximately 100 μm.

Step S305 is an aftertreatment step which is performed after theelectropolishing step S304. The aftertreatment step includes treatmentof discharging the electrolyte remaining inside the cavity main body 10to the outside, and cleaning treatment of cleaning the innercircumferential surface of the cavity main body 10 with hydrogenperoxide water or ultrapure water. In addition, the aftertreatment stepS305 includes treatment of removing the anode parts 230 and 240 and thecathode part 220 from the superconducting accelerating cavity 30.

After the aftertreatment step S305, the electropolished superconductingaccelerating cavity 30 is installed back into the vacuum vessel 90 tomake the superconducting accelerator 100 usable again.

Next, a modified example of the anode parts 230 and 240 will bedescribed by using FIG. 4. FIG. 4 is a view showing the modified exampleof the anode part installed in the refrigerant tank 20, and is anenlarged view of the cross-section of the superconducting acceleratingcavity 30 viewed from the front side. The anode parts 230 and 240described above are adapted such that the positions of the contact parts233 and 243 are adjusted by means of the male thread provided on theouter circumferential surfaces of the rod parts 232 and 242. Incontrast, an anode part 400 shown in FIG. 4 is adapted such that theposition of a contact part 403 is adjusted by means of the elastic forceof a coil spring 404.

As shown in FIG. 4, the anode part 400 of the modified example isconstituted of a cable connection part 401, a cap 402, a contact part403, the coil spring 404, and a metal spring 405. Each memberconstituting the anode part 400 is constituted of a highly conductivemetal such as copper. Each member constituting the anode part 400 issubstantially at the same potential as the positive pole of the powersource 250.

A cable coupled with the positive pole of the power source 250 isconnected to the cable connection part 401. The cable connection part401 is coupled with the cap 402. The cap 402 is fastened with a bolt tothe flange provided at the supply port 20 a or the discharge port 20 bof the refrigerant tank 20. The cap 402 is provided with a cylindricalportion, and the coil spring 104 having substantially the same diameteras the inner diameter of this cylindrical portion is inserted into thecylindrical portion.

The cylindrical contact part 403 having a larger inner diameter than theouter diameter of the cylindrical portion of the cap 402 is disposedaround the cylindrical portion. A biasing force in the direction ofbringing the contact part 403 into contact with the metal coating layer10 a of the cavity main body 10 is applied to the contact part 403 bythe coil spring 404 which is inserted in the cylindrical portion of thecap 402.

A metal spring 405 is provided between the outer circumferential surfaceof the cylindrical portion of the cap 402 and the inner circumferentialsurface of the contact part 403. The metal spring 405 allows the outercircumferential surface of the cylindrical portion of the cap 402 andthe inner circumferential surface of the contact part 403 to beelectrically connected with each other and reliably energized. Thebiasing force applied by the coil spring 404 causes the contact part 403to be disposed in contact with the metal coating layer 10 a of thecavity main body 10. Thus, the positive pole of the power source 250 andthe metal coating layer 10 a are electrically connected, so that themetal coating layer 10 a functions as an anode for electropolishing.

Next, another modified example of the anode parts 230 and 240 will bedescribed by using FIG. 5. FIG. 5 is a view showing the another modifiedexample of the anode part installed in the refrigerant tank 20, and isan enlarged view of the cross-section of the superconductingaccelerating cavity 30 viewed from the side surface (in the direction ofthe central axis). Description of the anode part 230 shown in FIG. 5,which is the same as the anode part 230 described in FIG. 2, will beomitted. FIG. 5 differs from FIG. 2 in that a contact point member 235is added.

The contact point member 235 is provided at the leading end of thecontact part 233, and is a member for improving the electrical contactbetween the contact part 233 and the metal coating layer 10 a. As thecontact point member 235, various materials, such as plain-knittedcopper wire or a copper leaf spring, etc., which can enhance electricalcontact can be used. The provision of the contact point member 235 makesit possible to improve the electrical contact between the contact part233 and the metal coating layer 10 a so that the metal coating layer 10a can more reliably function as an anode for electropolishing.

The contact point member 235 may also be provided at the leading end ofthe contact part 403 of the anode part 400 of the above-describedmodified example.

As has been described above, in the superconducting accelerating cavity30 of this embodiment, the outer circumferential surface of the cavitymain body 10 is coated, with the metal coating layer 10 a having ahigher conductivity than the superconducting material. Thus, accordingto the electropolishing method for the superconducting acceleratingcavity 30 of this embodiment, bringing the anode parts 230 and 240 intocontact with the outer circumferential surface of the cavity main body10 by the anode installation step S301 allows the cavity main body 10 tobe uniformly anodized for electropolishing.

Then, the cathode part 220 which is connected to the negative pole ofthe power source 250 is inserted into the cavity main body 10 by thecathode installation step S301, and the electrolyte is supplied into thecavity main body 10 by the electrolyte supply step S303, so that theinner circumferential surface of the cavity main body 10 can beelectropolished.

Thus, according to the electropolishing method for the superconductingaccelerating cavity 30 of this embodiment, it is possible to provide anelectropolishing method for a superconducting accelerating cavity bywhich electropolishing can be easily performed again even afterinstallation of the refrigerant tank 20.

The superconducting accelerating cavity 30 of this embodiment has ashape formed by the equatorial portions (large diameter portions) 10 d,10 e, 10 f, and 10 g, and the iris portions (small diameter portions) 10h, 10 i, and 10 j, which are at a shorter distance to the central axis Athan the equatorial portions 10 d, 10 e, 10 f, and 10 g, beingalternately formed along the axial direction. In addition, the positionof the refrigerant supply port 20 a in the axial direction correspondsto the position of the equatorial portion 10 d in the axial direction.Moreover, the position of the refrigerant discharge port 20 b in theaxial direction corresponds to the position of the equatorial portion 10g in the axial direction.

In this way, the anode part 230 inserted from the supply port 20 a canbe easily brought into contact with the equatorial portion 10 d of thecavity main body 10 which is disposed at the position close to thesupply port 20 a of the refrigerant tank 20. In addition, the anode part240 inserted from the discharge port 20 b can be easily brought intocontact with the equatorial portion 10 g of the cavity main body 10disposed at the position close to the discharge port 20 b of therefrigerant tank 20.

Second Embodiment

In the following, a cavity main body 600 of a superconductingaccelerator of a second embodiment will be described by using FIG. 6.FIG. 6 is a view showing the cavity main body 600 of a superconductingaccelerating cavity of the second embodiment of the present invention.Although the refrigerant tank is provided around the cavity main body600, the refrigerant tank is not shown in FIG. 6.

The second embodiment is a modified example of the first embodiment;unless otherwise described in the following, the second, embodiment isthe same as the first embodiment, and description thereof will beomitted.

The coating thickness of the metal coating layer 10 a of the firstembodiment is substantially constant regardless of the position in thedirection of the central axis of the cavity main body 10. In contrast,the coating thickness of a metal coaxing layer 600 a of the secondembodiment varies depending on the position in the direction of thecentral axis A of the cavity main body 600.

The cavity main body 600 shown in FIG. 6 includes equatorial portions(large diameter portions) 600 d, 600 e, 600 f, and 600 g at a distanceR3 from the central axis A. In addition, the cavity main body 600includes iris portions (small diameter portions) 600 h, 600 i, and 600 jat a distance R4 from the central axis A. As shown in FIG. 6, thedistance R4 to the central axis A of the iris portions 600 h, 600 i, and600 j is shorter than the distance R3 to the central axis A of theequatorial portions 600 d, 600 e, 600 f, and 600 g. As shown in FIG. 6,the cavity main body 600 has a shape formed, by the equatorial portions600 d, 600 e, 600 f, and 600 g, and the iris portions 600 h, 600 i, and600 j being alternately formed along the direction of the central axisA.

The outer circumferential surface of the cavity main body 600 is coatedwith a metal material having a higher conductivity than the superconducting material. This coated part forms the metal coating layer 600a. As the metal material having a high conductivity, for example,copper, gold, silver, or aluminum is used. The reason for coating theouter circumferential surface of the cavity main body 600 with a metalmaterial having a high conductivity is to make the cavity main body 600function as an anode during electropolishing.

As shown in FIG. 6, the coating thickness of the metal coating layer 600a varies depending on the position in the direction of the central axisA of the cavity main body 600. More specifically, the metal coatinglayer 600 a has a coating thickness T2 in the equatorial portions (largediameter portions) 600 d, 600 e, 600 f, and 600 g. On the other hand,the metal coating layer 600 a has a coating thickness T1 in the irisportions (small diameter portions) 600 h, 600 i, and 600 j. The coatingthickness T2 is larger than the coating thickness T1. The coatingthickness of the metal coating layer 600 a between the iris portionsadjacent to the equatorial portion has a shape gradually decreasing incoating thickness from the equatorial portion toward the iris portions.

An outlet part 600 b and an inlet part 600 c of the cavity main body 600are cylindrical openings. As shown in FIG. 6, the diameter of the innercircumferential surface of the outlet part 600 b and the inlet part 600c corresponds to the diameter of the inner circumferential surface ofthe iris portions 600 h, 600 i, and 600 j, and the each of the diametersis D1. On the other hand, the diameter of the inner circumferentialsurface of the equatorial portions 600 a, 600 e, 600 f, and 600 g is D2.

The ratio between the distance R3 to the central axis A of the innercircumferential surface of the equatorial portions and the distance R4to the central axis A of the inner circumferential surface of the irisportions, and the ratio between the coating thickness T2 of the metalcoating layer 600 a in the equatorial portions and the coating thicknessT1 of the metal coating layer 600 a in the iris portions correspond toeach other as expressed by the following equation (1), or substantiallycorrespond to each other.R4/R3−T1/T2  (1)

The reason for thus making the coating thickness of the metal coatinglayer 600 a thicker in the equatorial portions and making the coatingthickness of the metal coating layer 600 a thinner in the iris portionsis to substantially equalize the amount of polishing of the innercircumferential surface of the cavity main body 600 by electropolishingbetween the iris portions and the equatorial portions. As shown in FIG.2, the cathode is installed inside the cavity main body duringelectropolishing. Therefore, if the coating thickness of the metalcoating layer 600 a is constant along the central axis A, the amount ofpolishing of electropolishing becomes larger in the iris portions whichare closer to the cathode, while the amount of polishing ofelectropolishing becomes smaller in the equatorial portions which arefarther away from the cathode. In this embodiment, in order to reducethe difference in the amount of polishing between the iris portions andthe equatorial portions, the coating thickness of the metal coatinglayer 600 a is made thicker in the equatorial portions, and the coatingthickness of the metal coating layer 600 a is made thinner in the irisportions.

Making the coating thickness of the metal coating layer 600 a larger inthe equatorial portions allows the current to flow more easily to theequatorial portions. On the other hand, making the coating thickness ofthe metal coating layer 600 a smaller in the iris portions makes thecurrent flow relatively less easily to the iris portions. For example,by setting the coating thickness of the metal coating layer 600 a in theequatorial portions and the coating thickness of the metal coating layer600 a in the iris portions as expressed by the equation (1), thedifference in the amount of polishing between the iris portions and theequatorial portions can be reduced. While the coating thickness of themetal coating layer 600 a in the equatorial portions and the coatingthickness of the metal coating layer 600 a in the iris portions can beset, for example, as expressed by the equation (1), the coatingthicknesses can be appropriately set according to the various conditionsso that the amount of polishing is equalized between the iris portionsand the equatorial portions.

As has been described above, in the superconducting accelerating cavityof this embodiment, the cavity main body 600 has a shape formed by theequatorial portions (large diameter portions) and the iris portions(small diameter portions), which are at a shorter distance to thecentral axis A than the equatorial portions, being alternately formedalong the direction of the central axis A. In addition, the coatingthickness T2 of the metal coating layer 600 a in the equatorial portionsis larger than the coating thickness T1 of the metal coating layer 600 ain the iris portions.

In this way, current can flow more easily in the equatorial portionswhich are farther away from the central axis of the cavity main body600, in which the cathode is disposed during electropolishing, than inthe iris portions which are closer to the central axis. Thus, the defectof the degree of polishing of electropolishing becoming non-uniform inthe inner surface of the cavity main body 600 can be suppressed.

In the superconducting accelerating cavity of this embodiment, the ratiobetween the distance R3 to the central axis A of the equatorial portionsand the distance R4 to the central axis A of the iris portion, and theratio between the coating thickness T2 of the metal coating layer 600 ain the equatorial portions and the coating thickness T1 of the metalcoating layer 600 a in the iris portions correspond to each other orsubstantially correspond to each other.

In this way, the coating thickness T2 in the equatorial portions and thecoating thickness T1 in the iris portions of the cavity main body 600can be adjusted to a coating thickness according to the distance fromthe central axis of the cavity main body 600 in which the cathode isdisposed during electropolishing.

Other Embodiments

In the first embodiment, the anode part 230 is inserted into the supplyport 20 a and the anode part 240 is inserted into the discharge port 20b; however, the present invention may have a different aspect. Forexample, the anode part may be inserted into only one of the supply port20 a and the discharge port 20 b. Since the metal coating layer 10 a isevenly formed on the outer circumferential surface of the cavity mainbody 10, even when the anode part is inserted into only one of thesupply port 20 a and the discharge port 20 b, the entire outercircumferential surface of the cavity main body 10 can be at the samepotential as the positive pole of the power source 250.

The cavity main body 10 of the first embodiment shown in FIG. 1 isformed by four equatorial portions (large diameter portions) and threeiris portions (small diameter portions) being alternately formed alongthe central axis A; however, the present invention may have a differentaspect. For example, N equatorial portions and N−1 iris portions may bealternately formed (where N is an integer larger than, one).

The invention claimed is:
 1. A superconducting accelerating cavitycomprising: a cavity main body formed of a superconducting material intoa cylindrical shape; and a refrigerant tank installed around the cavitymain body and storing a refrigerant which is supplied from the outsidethrough a supply port into a space created between the refrigerant tankand the outer circumferential surface of the cavity main body, whereinthe outer circumferential surface of the cavity main body is coated witha metal material having a higher conductivity than the superconductingmaterial to make the cavity main body function as an anode duringelectropolishing, the cavity main body has a shape formed by largediameter portions and small diameter portions, which are at a shorterdistance to the central axis of the cavity main body than the largediameter portions, the large diameter portions and the small diameterportions being alternately formed along an axial direction, and thecoating thickness of the metal material in the large diameter portionsis larger than the coating thickness of the metal material in the smalldiameter portions.
 2. The superconducting accelerating cavity accordingto claim 1, wherein the cavity main body has a shape formed by largediameter portions and small diameter portions, which are at a shorterdistance to the central axis of the cavity main body than the largediameter portions, being alternately formed along the axial direction,and the position of the supply port in the axial direction correspondsto the position of the large diameter portion in the axial direction. 3.The superconducting accelerating cavity according to claim 1, whereinthe ratio between the distance to the central axis of the large diameterportions and the distance to the central axis of the small diameterportions, and the ratio between the coating thickness in the largediameter portions and the coating thickness in the small diameterportions substantially correspond to each other.
 4. An electropolishingmethod for a superconducting accelerating cavity comprising: a cavitymain body formed of a superconducting material into a cylindrical shape;and a refrigerant tank installed around the cavity main body and storinga refrigerant which is supplied from the outside through a supply portinto a space created between the refrigerant tank and the outercircumferential surface of the cavity main body, the outercircumferential surface of the cavity main body being coated with ametal material having a higher conductivity than the superconductingmaterial to make the cavity main body function as an anode duringelectropolishing, the electropolishing method comprising: inserting ananode part, which is connected to a positive pole of a power source,through the supply port and bringing the anode part into contact withthe outer circumferential surface of the cavity main body; inserting acathode part, which is connected to a negative pole of the power source,into the cavity main body; supplying an electrolyte into the cavity mainbody; and starting energization by the power source and electropolishingthe inner surface of the cavity main body.
 5. The electropolishingmethod for a superconducting accelerating cavity according to claim 4,wherein the cavity main body has a shape formed by large diameterportions and small diameter portions, which are at a shorter distance tothe central axis of the cavity main body than the large diameterportions, being alternately formed along an axial direction, and theposition of the supply port in the axial direction corresponds to theposition of the large diameter portion in the axial direction.
 6. Theelectropolishing method for a superconducting accelerating cavityaccording to claim 4, wherein the cavity main body has a shape formed bylarge diameter portions and small diameter portions, which are at ashorter distance to the central axis of the cavity main body than thelarge diameter portions, being alternately formed along an axialdirection, and the coating thickness of the metal material in the largediameter portions is larger than the coating thickness of the metalmaterial in the small diameter portions.
 7. The electropolishing methodfor a superconducting accelerating cavity according to claim 6, whereinthe ratio between the distance to the central axis of the large diameterportions and the distance to the central axis of the small diameterportions, and the ratio between the coating thickness in the largediameter portions and the coating thickness in the small diameterportions substantially correspond to each other.